This invention relates to novel polypropylene compositions characterized by high stiffness, good toughness, and high ignition resistance.
Polypropylene, which is readily available at a reasonable cost, has found many industrial uses because of its desirable physical properties such as ease of fabrication by all conventional methods; high melting point of stereoregular, e.g., isotactic, polypropylene; and compatibility with many other commercial resins, which permits a large number of blends having specific properties. Isotactic polypropylene is inherently brittle, that is, it has a low impact resistance. Brittleness can be reduced either by copolymerizing propylene with ethylene to form block copolymers or by blending homopolypropylene with rubber, for example with EPM or EPDM elastomers. These elastomers are well known to the art. They are copolymers of ethylene with propylene and in the latter case, one or more diene monomers, at least one of which has double bonds that polymerize at different rates.
These copolymers or blends have found many applications, including automobile parts and electric wire insulation. However, one of the problems encountered in applications where fire hazards may be encountered is the lack of ignition resistance of such copolymers or blends. Where sufficient amounts of flameproofing ingredients have been added, those compositions usually have unsatisfactory mechanical properties in that either their impact resistance or stiffness are too low for their intended application.
Accordingly, it is highly desirable to provide a polypropylene composition which would not suffer from such drawbacks.